For over two centuries asteroids were just points of light in telescopes (hence the term asteroid, which means "starlike"). Until recently, that is: we're a spacefaring race now, and we can send our robots to sniff out these giant rocks up close... and in July, the European Space Agency probe Rosetta flew past the asteroid Lutetia, returning amazing close-ups of the rock.

This picture, which I borrowed from my friend Emily Lakdawalla at the Planetary Society Blog (I fiddled with the contrast and brightness a bit to bring out the darker side) was taken at closest approach. Lutetia is about 130 km (80 miles) across, and is the largest asteroid we've visited. You can see it's a lumpy, battered, rock, pitted with craters. The details are stunning: giant boulders held by the weak gravity dot the surface, parallel grooves mark stress fractures in the surface (or secondary deposits of material ejected from impacts?), and shadows highlight the contours.

We're just beginning to understand the nature of asteroids - and given that every now and again one of them pays Earth a catastrophic visit (just ask the dinosaurs) - it's good idea that we learn as much about them as we can.